Electrical switch device having a fed liquid-metal cathode and a non-intercepting anode

ABSTRACT

The electrical switch device has an envelope in which is mounted a liquid-metal cathode, an anode, and a condenser. The cathode is capable of very high electron-to-atom emission ratio. A desirable value for the electron-to-atom emission ratio is on the order of 100 or more and is attainable by means of a cathode such as disclosed in U.S. Pat. No. 3,475,636, when used in the switch device. The condenser has a very much larger area than the exposed liquid metal area on the cathode, and it is kept at a low enough temperature to efficiently condense the liquid-metal vapor emitted by the cathode. With mercury used as the liquid metal, the condenser temperature is kept substantially below 0* C., preferably at about -35* C. which is just above the melting point of mercury. When arcing occurs from the liquid metal, a plasma jet of electrons, ions, and neutral particles is emitted from the arc spot. The anode is mounted between the cathode and the condenser, and it is positioned at the edge of the plasma jet to capture the major portion of the electron flow for electrical conduction. Most of the ions and neutral particles as well as a sufficient number of electrons to preserve space-charge and current neutrality, pass the anode in the plasma jet and are captured on the condenser. The combination of the high electronto-atom emission ratio of the cathode with the large, lowtemperature condenser results in an equilibrium background pressure (i.e., pressure outside the plasma jet) of at least as low as 10 3 Torr during arcing, and lower than 10 4 Torr during non-arcing periods. These low pressures are obtained by maintaining the condenser in the range of low temperatures defined above. This low background pressure, in turn, permits the essentially unperturbed propagation of the plasma jet between the cathode and the surfaces upon which it impinges, i.e., condenser and anode. Such a discharge mode is commonly referred to as a &#39;&#39;&#39;&#39;vacuum arc.&#39;&#39;&#39;&#39; The fact that the plasma jet is emitted only during arcing, and that the pressure within the space surrounding this jet is kept low, results in the ability to hold off electric fields up to 50 kV per centimeter between anode and cathode immediately after cessation of arcing.

United States Patent Lian et al.

[451 June 6, 1972 ELECTRICAL SWITCH DEVICE 1968, abandoned.

[52] US. Cl ..3l3/7, 313/34, 313/167, 313/173 [51] Int. Cl. .1101] 1/10,HOij 7/16 [58] Field ofSeai-ch ..313/7, 29, 33, 34, 163, 167,

[56] References Cited UNITED STATES PATENTS 1,865,512 7/1932 Gaudenzi eta1. ..3l3/34 X 2,189,635 2/1940 Klemperer .313/34 X 2,205,231 6/1940Steenbeck ..313/34 3,475,636 10/1969 Eckhardt ..313/29 PrimaryExaminer-Roy Lake Assistant ExaminerPalmer C. Demeo Attorney-James K.Haskell and Allen A. Dicke, Jr.

57 ABSTRACT The electrical switch device has an envelope in which islsclotor mounted a liquid-metal cathode, an anode, and a condenser. Thecathode is capable of very high electron-to-atom emission ratio. Adesirable value for the electron-to-atom emission ratio is on the orderof 100 or more and is attainable by means of a cathode such as disclosedin US. Pat. No. 3,475,636, when used in the switch device. The condenserhas a very much larger area than the exposed liquid metal area on thecathode, and it is kept at a low enough temperature to efficientlycondense the liquid-metal vapor emitted by the cathode. With mercuryused as the liquid metal, the condenser temperature is keptsubstantially below 0 C., preferably at about 35 C. which is just abovethe melting point of mercury. When arcing occurs from the liquid metal,a plasma jet of electrons, ions, and neutral particles is emitted fromthe are spot. The anode is mounted between the cathode and thecondenser, and it is positioned at the edge of the plasma jet to capturethe major portion of the electron flow for electrical conduction. Mostof the ions and neutral particles as well as a sufficient number ofelectrons to preserve space-charge and current neutrality, pass theanode in the plasma jet and are captured on the condenser. Thecombination of the high electronto-atom emission ratio of the cathodewith the large, low-temperature condenser results in an equilibriumbackground pres sure (i.e., pressure outside the plasma jet) of at leastas low as 10' Torr during arcing, and lower than 10" Torr duringnonarcing periods. These low pressures are obtained by maintaining thecondenser in the range of low temperatures defined above. This lowbackground pressure, in turn, permits the essentially unperturbedpropagation of the plasma jet between the cathode and the surfaces uponwhich it impinges, i.e., condenser and anode. Such a discharge mode iscommonly referred to as a vacuum arc. The fact that the plasma jet isemitted only during arcing, and that the pressure within the spacesurrounding this jet is kept low, results in the ability to hold offelectric fields up to 50 kV per centimeter between anode and cathodeimmediately after cessation of arcing.

PATENTEnJun 61972 SHEET F 2 Fig. 1.

-lsolator V so I 1 42 4 78 I fin 50 E Z 44 Kenneth T. Lion, 54-. RonaldC.Knechrli,

INVENTORS. 2s 58) BY.

LM 60 L," ALLEN A.DlCKE,Jr.,

AGENT.

PATENTEnJun 6 I972 3. 668,453

sum 2 or 2 Fig 4.

Kenneth T. Lian, Ronald C. Knechrli,

INVENTORS.

ALLEN A. DICKE, Jr.,

AGENT.

ELECTRICAL SWITCH DEVICE HAVING A FED LIQUID- METAL CATl-IODE AND ANON-INTERCEPTING ANODE CROSS REFERENCE This application is acontinuation-in-part of U.S. Pat. application Ser. No. 720,692, filedApr. 1 1, 1968, now abandoned. This application is related to U.S. Pat.application Ser. No. 51,868, filed July 2, 1970.

BACKGROUND OF THE INVENTION This invention is in the field of mercuryarc electrical devices where an arc extends from a cathode to an anode,to permit electron current flow therebetween.

Prior art devices which permit rectification and inversion by means of amercury are are well known. These prior devices employ a large mercurypool against which the arc strikes. However, the prior devices are verylimited in the amount of forward and reverse voltage standoff betweenthe anode and cathode because of the presence of the large mercury pool.The pressure within the tube is fairly high, because of the evaporationfrom the mercury pool, even though the mercury pool temperature is keptas low as is possible consistent with arcing. The relatively highmercury vapor pressure in such tubes, when nonconducting, limits thepermissible peak forward and reverse voltage as well as the recovery anddeionization rates. An example of such structures is shown in SteenbeckU.S. Pat. No. 2,205,231. To overcome this limitation, state of the arthigh voltage mercury tubes are provided with grading electrodes. Thesegrading electrodes lead to another limitation: the current which canpass to one anode through such a set of grading electrodes'is limited tosuch extent that for higher currents, a number of parallel anodes andsets of grading electrodes are required. These limitations thus lead tothe need for complex multi-anode tubes, with current dividingtransformers to divide the current uniformly between parallel anodes,and grading electrodes with attendant voltage dividers.

The voltage holdofi properties of the conventional mercury pool liquidcathode devices are determined by a tradeoff between the desired voltageholdoff, and the peak current, the voltage drop across the arc andvoltage recovery rates. These conflicting requirements do not permit thedevice to be designed for high voltage holdofi and high current withoutthe complex grading electrodes and the multiple anodes mentioned above.

SUMMARY OF THE INVENTION I In order to aid in the understanding of thisinvention, it can be stated in essentially summary form that it isdirected to an electrical switch device having a force fed liquid-metalcathode, an anode and a condenser positioned within an enclosure. Thecathode has metal in other than a solid state fed thereto to maintain asmall pool or film of liquid metal for electrical arcing. The condensermaintains the background pressure in the vessel below 10' Torr duringarcing so that arcing occurs in the vacuum arc mode wherein neutralparticles, electrons and ions are expelled in a fairly well definedplasma cone from the arc spot, at an electron-to-atom emission ratio onthe order of 100 to l. The condenser is positioned in the path of theplasma jet cone to capture essentially the entire metal atom and ionefilux jetting from the cathode spot. The anode is positionedintermediate the cathode and condenser at the edge of the plasma jetcone to capture the electron flow for electrical conduction between thecathode and anode. In order to maintain the vacuum arc mode ofdischarge, and in order to maintain high holdofi' of electric fieldsduring nonarcing, when mercury is used as a liquid metal, the condenseris maintained at a temperature below C, preferably as low as about 35 C.so as to provide an envelope pressure of as low as about 5 X Torr duringnonarcing.

It is thus an object of this invention to provide an electrical highvoltage, high current, single gap switch device which has a smallliquid-metal cathode emitting a substantially conical plasma jet and ananode structure positioned with respect to the cathode so that the anodedoes not directly intercept the conical plasma jet emitted from thecathode. It is further object to provide an enclosed switch device withthe background pressure maintained therein at a sufficiently low level,such as 10 Torr or less during arcing, that it does not interfere withthe plasma jet cone so that the plasma jet cone is not distorted and ananode structure can be positioned with respect to the plasma jet cone atthe boundary of the plasma jet to prevent substantial interference withthe jet cone. It is another object of this invention to provide anenclosed switch tube having an anode structure, a cathode and acondenser and arranged so that the condenser, optionally together withvacuum pumping devices, maintains the pressure within the tube at asufficiently low level that the pressure in the tube does not interferewith the flow of neutrals and ions from arc spots, so an anode structurecan be positioned with respect to the plasma jet cone and at theboundary of the plasma jet cone issuing from the are spot. It is afurther object of this invention to provide a liquidmetal cathode whichis fed with non-solid metal so that a small area of liquid metal isprovided for arcing activity which area defines the position of arcingactivity and thus defines the apex of the plasma cone issuing from theliquid-metal area to accurately define the plasma cone position and thuspermit anode positioning with respect to the plasma cone. It is afurther object of this invention to provide a liquid-metal cathode whichis fed with non-solid metal so that a small area of liquid metal isprovided for arcing activity. Other objects and advantages of thisinvention will become apparent from a study of the following portion ofthe specification, the claims and the attached drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of an electricalswitch device having a liquid-metal cathode and having an anode shapedand positioned in accordance with this invention.

FIG. 2 is a vertical section therethrough.

FIG. 3 is an enlarged, partial vertical section showing a portion of thecathode and a portion of its associated anode.

DESCRIPTION The electrical switch device of this invention is generallyindicated at 10 in FIGS. 1 and 2. The electrical switch device has acathode 12, an anode 14 and a condenser 16 positioned within vessel 18.The vessel is closed so that a low pressure can be maintained interiorlythereof. Vacuum pump connection 20 is optionally provided for thepurpose of aiding maintenance of the low pressure necessary for properoperation of the switch device.

It is essential that the cathode 12 be the type of cathode taught inU.S. Pat. No. 3,475,636. Any one of the cathode embodiments illustratedin that patent can be employed, or any other specific cathodeconfiguration falling within the teachings of that patent is usefulherein.

Cathode 12 is illustrated in more detail in FIG. 3 wherein cathode body22 has liquid-metal passage 24 therein. Passage 24 terminates in flowrestriction 26 which can either take the form of the porous plug shown,or of a narrow capillary flow control tube or any other fiow impedance.Liquid metal is made to pass through passage 24 and through flowrestriction 26. One method of accomplishing this is by use ofliquid-metal pump 28 which delivers liquid metal through line 30. Anexample of such a pump is shown in H. J. King, U.S. Pat. No. 3,444,816.If recirculation is required, the metal can be drawn from condenser 16.In such a case electrical isolator 32 is inserted in line 30. Saidisolator 32 can be of the type taught in H. J. King et al, U.S. Pat. No.3,443,570. Ari evaporative type transport system or a suitably arrangedgravity feed system could optionally be used to transfer the liquidmetal from the vessel 18 to the electrical isolator 32. In some cases,no heating is required to maintain the metal in its liquid state as itis delivered to passage 24, but in other cases, heating may be necessaryto maintain the liquid state. The question of whether or not heating isemployed is dependent upon the choice of the metal, and the ambientconditions.

In the case of mercury, the specified condenser temperature is keptsubstantially below C. In the case of mercury, a preferred condensertemperature is about 35 C., this being just above the melting point ofmercury and permitting the maintenance of a background pressure as lowas 5 X Torr during non-arcing conditions. The cathode is cooled astaught in U.S. Pat. No. 3,475,636 so as to keep its evaporation from theliquid metal into the background atmosphere negligible during non-arcingconditions. Such evaporation is said to be negligible when the pressureof the background atmosphere is approximately equal to the vaporpressure of the liquid metal at the condenser temperature, this vaporpressure being ap proximately 5 X 10 Torr for mercury at a temperatureof 35 C. Of course, during arcing the cathode heats up with the resultthat the pool of mercury is above that temperature. However, the poolsize is sufficiently small in comparison to -the size of the condenserthat during arcing the background pressure is maintained at at least aslow as 10 Torr- When heating is necessary for metals other than mercuryto maintain the liquid state, such heating can be applied to the pump,the isolator and the connecting line 30. Additionally, heating orcooling of the cathode body 22 may be necessary to maintain the cathodeat proper operating temperature, depending on thechoice of liquid metal,the cathode current, heat losses to the atmosphere, and the like.

The front of cathode 12, in front of flow restriction 26, haspool-retaining walls 34. These pool-retaining walls are preferablyconical, and are preferably formed with the total included angle of theapex of the cone of approximately 60 or more. The apex of the cone ispositioned at the face of flow restriction 26. In the downward directionin FIG. 3, below the conical area, the walls are curved outward topresent a substantially planar front face 36. For further details of theconstruction and operation, attention is drawn to W. O. Eckhardt U.S.Pat. No. 3,475,636, the entire disclosure of which is incorporatedherein by this reference.

As is seen in FIG. 2, cathode 12 is insulated from the anode 14 by meansof insulator 38. Insulator 38 is sealed to both the anode and cathode toprovide closure of the interior of the device 10 from the externalatmosphere. The front face 36 is formed on the front of a skirt 40 whichextends outwardly and up into the interior of the space enclosed byinsulator 38. This skirt helps to prevent deposition of liquid-metalparticles on the insulator adjacent the cathode and protects thejunction between insulator 38 and cathode 12 from high electric fields.

Anode structure 14 is annular and is substantially coaxial with theaxial center line of cathode 12. The interior surface 42 of anode 14 isgenerally in the form of a truncated cone, smoothed into faired out withrounded edges at top and bottom. The interior surface 42 is arrangedwith approximately a 40 to 70 total included conical angle, similarly tothe angle of the plasma cone emitted from the cathode as describedbelow. The interior surface 42 lies adjacent to the plasma cone for goodelectrical coupling. This relates the interior surface 42 of the anodeand the outside of the jet formed from the liquidmetal pool positionedbetween pool-retaining walls 34. The skirt 40, anode l4 and insulator 38are maintained at a temperature such that metal vapor will not condenseon these surfaces. I

' Anode 14 is mounted upon insulative support ring 44 which is securedto anode 14 on its upper side, and is secured to the body of vessel18.on its lower side. Connector 46 extends outwardly from anode 14 topermit electrical connection thereto. Heat exchanger 47 controls anodetemperature. Skirt 48 extends upward from anode 14 into the space on theinterior of insulator 38, and substantially parallel to skirt 40, toprotect the junction between insulator 38 and the anode 14 from highelectric fields and sputtered deposition. Anode structure 14 maycomprise an anode structure having plurality of electrically separateelectrodes for special electrical connection such as polyphaserectification.

Condenser 16 is built up of a plurality of thin truncated conical shellsor fins which are coaxially arranged with cathode 12. Condenser 16 canbe mounted on legs in the bottom of vessel 18, or by any otherconventional, convenient support structure. Alternatively, it can alsoconsist of a single cup-shaped container or of a container in the formof a closed box with an appropriate opening to permit entrance andcapture of the plasma jet past the anode. Again, the total included coneangle is approximately 60 to 70 so that the shells are arranged edgewiseto material flow. Conical shells 50 are mounted on top of shells 52which are cylindrical tubes. The shells 50 and 52 are cooled byappropriate cooling means such as circulating coolant which flowsthrough jacket 54 through connections 56 and 58. The shells aremaintained at a suitably low temperature to condense metal vapor intothe liquid or optionally the solid state and permit it togravitationally discharge out of the bottom of vessel 18. Drainageopenings at the bottoms of shells 58 permit the condensed liquid metalto drain so that it moves through line 60 to liquid-metal pump 28 or anyother appropriate recirculating means or other appropriate means ofdisposition.

The term liquid metal is used to define those metals which are liquid ator somewhat above room temperature. While called liquid metal,'it is notnecessarily in the liquid state when fed to the pool-keeping surfaces.Mercury is a convenient liquid metal because it is normally liquid atroom temperatures. Additionally, cesium, lithium, and gallium are alsoexamples of suitable materials to act as the liquid metal. If necessary,the liquid-metal circulating system can be heated to maintain theliquidity of the liquid metal, as is discussed above.

Cathode 12 and anode 14 are preferably of refractory metal. When mercuryis employed as the liquid metal, molybdenum serves as a suitablematerial for the anode and cathode. Liquid metal is pumped through inletpipe 30 to cathode 12, to form a small pool 76, see FIG. 3, which isretained between walls 34. Alternatively, liquid-metal vapor is fed tothe poolkeeping walls, whereon it transiently condenses.

U.S. Pat. No. 3,475,636 discloses the cathode in more detail. Any one ofthe cathodes disclosed in that Eckhardt patent is useful herein. Thepool-keeping walls are indicated at 34, and the liquid metal isdelivered thereto. When a liquid pool is employed, it rests in the conebetween the pool-keeping walls and is as small a pool as possible,consistent with reliable arcing.

When liquid metal vapor is fed through passage 24, see F IG. 3, flowrestriction 26 is normally not necessary, the passageway itselfproviding the flow control pressure drop. The passageway 24 can be quitesmall in diameter, and enter directly into the apex of the cone definedby pool-keeping walls 34. When liquid metal vapor is fed, thepool-keeping walls 34 are maintained at a temperature where transientcondensation occurs. This is a temperature within a few degrees aboveequilibrium temperature so that vapor molecules can stick to the surfacefor a short time, but cannot build up into a layer which ismultimolecule thick. In such a case there is no pool" which comprises adrop of liquid mercury, but instead, molecules of mercury upon thesurface of walls 34 supply the liquid metal for arcing. Under thecircumstances, these walls 34 can be larger in physical size, althoughthe amount of mercury transiently condensed thereon is preferably farless than the surface coverage. This method of feeding liquid metal to acathode is disclosed in more detail in U.S. Pat. application Ser. No.720,694, filed Apr. ll, 1968', entitled Vapor Feeding of Liquid MetalCathodes by Wilfried O. Eckhardt, now U.S. Pat. No. 3,538,375, grantedNov. 3, l970,the entire disclosure of which is incorporated herein bythis reference.

The pressure within vessel 18 is maintained sufficiently low that whenarcing occurs, it occurs in the vacuum arc mode.

The vacuum arc mode is broadly defined as an arc having electrons,positive ions and neutrals supplied in a plasma jet by are spots withina vessel having a background press'iire sufficiently low that it doesnot substantially affect the trajectories of the atoms and ions in thisplasma jet. In the vacuum arc mode there must be negligible permanentgas (outside of the arcing material) present in the arc. Thus, when thearc becomes extinguished, the pressure in the arc space returns to asufficiently low value to provide high electric field holdoff. Tomaintain a vacuum arc mode of operation, the vessel must not containlarge areas of liquid metal or other material available for evaporationinto the atmosphere of the vessel.

The background pressure in the vessel during non-arcing and duringarcing is sufficiently low that the mean free path of the gas moleculesor atoms of the background gas is large compared with the greatestdimension of the arc. The vacuum arc is therefore dependent for theatmosphere in which it burns on the emission of metal vapor and plasmafrom its cathode spots in the form of a plasma jet. This plasma jetbeing essentially electrically neutral because of the presence of asufficient number of the positive ions to substantially neutralize theelectronic space charge, the discharge runs at a low arc voltage.

Current between the plasma jet and the anode is carried by the plasmaelectrons reaching the anode. Current between cathode and plasma jet isbelieved to be carried both by electrons emitted from the cathode and byions falling back from the cathodes spots to the cathode. Neutral metalvapor in the efflux from the cathode condenses on the condenser, as wellas ions reaching the condenser from the plasma jet.

Conditions in the vacuum arc plasma are characterized largely by thefact that the vacuum arc depends for its plasma on the metal vaporemitted from its own cathode spots, and that this plasma and metal vaporare emitted from the region of the cathode spots in the form of a jet,called here the plasma jet." It is by these characteristics that thevacuum arc differs most markedly from the more common low pressure arc.

The pressure within vessel 18 is maintained sufficiently low that whenarcing occurs, it occurs in the vacuum arc mode. As discussed above, thevacuum arc mode is broadly defined as having electrons, positive ionsand neutrals supplied by the arc spots, the background pressure withinthe vessel being sufficiently low that it does not substantially affectthe trajectories of the atoms and ions emitted from the are spot. Morecomplete discussion of the vacuum arc and of the arcing voltage metalsis found in the Proceedings of the Institute of Electrica! Engineers,Vol. 1 10, No. 4, Apr. 1963, pages 793-802. in this specification, arcvoltage and arcing voltage are interchangeably used. To provide thevacuum are conditions described above, the pressure in the backgroundvolume outside of the plasma jet should not exceed about 10 Torr. Inorder to keep the pressure at 10 Torr or less in the background volumeoutside of the plasma jet during arcing, a condenser temperature ofabout l C. or less is necessary when mercury is used as the liquidmetal. A preferred condenser temperature for mercury is about -35 C.,which corresponds to just-liquid mercury on the condenser surface, andpermits to attain a pressure as low as 5 X Torr during nonarcing.

The are is initiated by any convenient means, including those well knownin the art, such as auxiliary electrode igniters, semiconductorigniters, and the like. Alternatively, a laser igniter directed onto theliquid-metal surface is suitable, but schematically illustrated isigniter 86 which emits a pufi of plasma into the space between the anodeand the cathode to initiate arcing. Plasma puffers are well known. Oneis described in detail in an article by Winston H. Bostick, entitledPlasma Motors," at pages 169 through 178 in the proceedings of theConference on Extremely High Temperatures, edited by Fischer and Mansurand published by Wiley, 1958. Other suitable igniters are disclosed inGaseous Conductors" by James D. Cobine, Dover Publications, New York,1941, particularly at pages 42 l-426. Once the arc is initiated,

a plasma jet is emitted from the cathode. This plasma jet containselectrons, ions and neutral particles. The jet issues from the are spoton the liquid metal and issues forth in a solid cone having a cone angleof about 60 to The interior surface 42 of anode 14 is positioned in suchrelationship with the plasma cone that it does not substantiallyinterfere with the progress of ions and neutral particles to thecondenser. The condenser rapidly captures these particles, so that thebackground pressure inside of vessel 18 remains low. Furthermore, thesmall liquid metal area adjacent to wall 34 is sufficiently small andmaintained at sufficiently low temperature that the evaporationtherefrom does not adversely affect the pressure inside the vessel, thispressure being maintained suffciently low that vacuum are conditions aremaintained, that there is no substantial interference with the highvelocity of the plasma jet, and that low enough pressure can bemaintained to prevent breakdown. Electrons are extracted from the plasmacone and captured on anode 42 to thus cause current conduction.

The advantage of vacuum arc operation as defined above, is that whenarcing ceases, the high velocity jet of particles from the arc spot israpidly captured on the condenser so that the space between the anodeand the cathode very quickly is returned to vacuum conditions whereinthe vacuum has high insulative value. This permits rapid application ofreverse voltage vvithout conduction, at a rate of voltage rise up to 10kilovolts per microsecond or even more. This makes the electrical switchdevice 10 of great utility for high voltage rectification, controlledrectification, and inversion, particularly at high currents.

The cessation of arcing can occur in operation by the change in polarityapplied to the terminals. Additionally, cessation of arcing can be madeto occur by stopping the flow of liquid metal to the liquid-metal pool76. Thus, the device is useful for dc switching, for when it is desiredthat current be stopped, the liquid-metal flow is stopped to starve thepool and thus cause cessation of arcing. The material of the cathodearound the pool is of such high are voltage that the arc is extinguishedrather than transferred to this material. To maintain stable currentflow in the device under the desired condition of high electron-to-atomemission ratio at the cathode, it is desirable to operate atapproximately constant electron-to-atom emission ratio. To this effect,the feeding of the liquid metal must be proportional to the arc current.When the average current is constant, the liquid metal can be fed at aconstant rate. Additionally, the electrical switching device 10 can actas an overcurrent fault protector. When an adequate amount of liquidmetal is fed in an amount proportional to normal current, up to apredetermined maximum feed rate of liquid metal is fed to the cathode tosupply normal current needs; when a fault occurs which draws a largeramount of current, the liquid-metal pool rapidly becomes exhaustedbecause of its small volume. When the pool is exhausted, again arcingstops so that excessively high fault currents can be interrupted. Ofcourse, modulated feeding of the liquid metal produces controlled forcedcurrent interruption when the current starves the pool.

This invention having been described in its preferred embodiment, it isclear that it is susceptible to numerous modifications and embodimentswithin the ability of those skilled in the art and without the exerciseof the inventive faculty.

What is claimed is:

1. An electrical switch device, said electrical switch devicecomprising:

a vessel;

cathode means within said vessel for issuing electrons, ions,

and neutral particles, said cathode means having a high are voltagematerial wall;

means for feeding a low arc voltage metal in other than the solid stateto a position adjacent said wall so that low arc voltage metal is onsaid wall;

anode means within said vessel for receiving electrons from said cathodemeans;

condenser means having a condensing surface within said vessel forreceiving and condensing ions and neutrals, said condensing surface ofsaid condenser means (a) having a sufficiently large area with respectto the low arc voltage metal on said wall of said cathode means, (b)being positioned with respect to said cathode means and anode means andbeing maintained at a sufiiciently low temperature to cause the interiorof said vessel to be maintained at a sufficiently low pressure, and (d)said cathode means, anode means, and condenser means being operated forcausing an electric discharge between said cathode means and said anodemeans in a vacuum are mode wherein an are spot is formed on the low arcvoltage metal on said wall and a plasma cone is ejected from the arespot to issue directly toward said condenser means, the plasma conecontaining electrons, ions and neutral particles so that said condensermeans condensing substantially all of the neutral particles and ionsemitted from the arc spot so that said condenser means maintains thebackground pressure within said vessel sufficiently low that theatmosphere in said vessel does not substantially interfere with theplasma cone so that discharge in a vacuum arc mode is maintained;

said anode means being positioned between said cathode means and saidcondenser means and having an anode wall defining an openingtherethrough, said anode wall being positioned substantially tangent tothe plasma cone to minimally perturb the ions and neutral particles inthe plasma cone and to electrically couple said anode means with theplasma cone.

2. The electrical switch device of claim 1 wherein said condenser meansis maintained below 0 C. to maintain a pressure within said vesseloutside of the plasma cone at least as low as Torr during arcing andlower than 10 Torr during nonarcing.

3. The switch tube of claim 1 wherein said high are voltage materialwall in said cathode is substantially conical, said substantiallyconical cathode wall defining an axis, said anode means being positionedsubstantially coaxially with respect to said axis, said anode wall beingsubstantially conical and being positioned adjacent the plasma coneemitted from low arc voltage material on the cathode wall. 1

4. The electrical switch device of claim 3 wherein said anode means hasan annular body having an interior frustoconical surface, said interiorsurface of said anode body having its apex substantially at said higharc voltage material wall of said cathode.

5. An electrical switch device comprising:

a vessel;

condenser means having a condensation surface within said vessel forcondensing ions and neutral particles in said vessel to maintain asufficiently low background pressure within said vessel during arcingthat the atmosphere in said vessel does not substantially interfere witharcing so that a conical plasma jet containing electrons, ions, andneutral particles is formed, so that electric arc discharge in a vacuumarc mode can be maintained, said condensation surface being positionedin the path of the conical plasma jet;

cathode means within said vessel for carrying a low arc voltage metal insufiiciently small area to minimize evaporation of low arc voltage metalfrom said cathode means into the atmosphere within said vessel to permitsaid condenser means to maintain the background pressure within saidvessel during arcing sufiiciently low so that the plasma jet is an arcdischarge in a vacuum arc mode; anode means within said vessel forinteracting with said cathode means by collecting electrons from theplasma jet so that an electric arc discharge in a vacuum arc mode ismaintained from the low arc voltage metal on said cathode means to saidanode means, said anode means being formed with a conical anode walldefining an opening therethrough, with said anode wall positionedsubstantially tangent to the conical plasma jet so as to minimallyperturb the ions and neutrals in the plasma cone and so as toelectrically couple said anode structure with the plasma cone.

6. The electrical switch device of claim 5 wherein:

said condenser means has a sufficiently large area with respect to thelow arc voltage metal area on said cathode means and beingpositionedwith respect to said cathode means and said anode means for maintenanceof the background pressure within said vessel during arcing outside ofthe conical plasma jet, at least as low as 10' Torr so that the arcoccurs in the vacuum arc mode and the atmosphere in said vessel does notsubstantially interfere with the conical plasma jet.

7. The switch device of claim 6 wherein said condenser means hassufficiently large condenser surface area with respect to the low arcvoltage metal on said cathode means and is maintained at least as low asabout 263 K; so that pressure within said vessel outside of the conicalplasma jet is not higher than about 10' Torr during arcing and nothigher than about 10' Torr during non-arcing.

8. The electrical switch device of claim 7 wherein said cathode means isoperated so that the ratio of electrons to atoms within said conicalplasma jet is at least as high as about fifty. 9. The switching deviceof claim 5 wherein said surface on said anode means comprises atruncated hollow cone with its apex substantially at the lower arcvoltage metal on said cathode means.

10. The process of switching an electric current comprising the stepsof:

maintaining a vessel in which is positioned a condenser surface ofsufficient size to dominate the vapor equilibrium in said vessel at areduced pressure by maintaining the condenser surface at a reducedtemperature;

feeding liquid metal to a cathode in the vessel for conducting electriccurrent by arcing;

cooling the condenser surface to a sufiiciently reduced temperature sothat arcing which occurs between the cathode and an anode in the vesselis in a vacuum arc mode;

discharging an are between the anode and cathode which produces a plasmajet containing electrons, ions and atoms with the ratio of electrons toatoms being at least 30-1; and v directing the plasma jet through theanode toward the condenser so that the anode lies substantially tangentto the plasma jet so that the anode is directly electrically coupledwith the plasma jet for electron flow from the plasma jet to the anode.

1. An electrical switch device, said electrical switch devicecomprising: a vessel; cathode means within said vessel for issuingelectrons, ions, and neutral particles, said cathode means having a higharc voltage material wall; means for feeding a low arc voltage metal inother than the solid state to a position adjacent said wall so that lowarc voltage metal is on said wall; anode means within said vessel forreceiving electrons from said cathode means; condenser means having acondensing surface within said vessel for receiving and condensing ionsand neutrals, said condensing surface of said condenser means (a) havinga sufficiently large area with respect to the low arc voltage metal onsaid wall of said cathode means, (b) being positioned with respect tosaid cathode means and anode means and (c) being maintained at asufficiently low temperature to cause the interior of said vessel to bemaintained at a sufficiently low pressure, and (d) said cathode means,anode means, and condenser means being operated for causing an electricdischarge between said cathode means and said anode means in a vacuumarc mode wherein an arc spot is formed on the low arc voltage metal onsaid wall and a plasma cone is ejected from the arc spot to issuedirectly toward said condenser means, the plasma cone containingelectrons, ions and neutral particles so that said condenser meanscondensing substantially all of the neutral particles and ions emittedfrom the arc spot so that said condenser means maintains the backgroundpressure within said vessel sufficiently low that the atmosphere in saidvessel does not substantially interfere with the plasma cone so thatdischarge in a vacuum arc mode is maintained; said anode means beingpositioned between said cathode means and said condenser means andhaving an anode wall defining an opening therethrough, said anode wallbeing positioned substantially tangent to the plasma cone to minimallyperturb the ions and neutral particles in the plasma cone and toelectrically couple said anode means with the plasma cone.
 2. Theelectrical switch device of claim 1 wherein said condenser means ismaintained below 0* C. to maintain a pressure within said vessel outsideof the plasma cone at least as low as 10 3 Torr during arcing and lowerthan 10 4 Torr during non-arcing.
 3. The switch tube of claim 1 whereinsaid high arc voltage material wall in said cathode is substantiallyconical, said substantially conical cathode wall defining an axis, saidanode means being positioned substantially coaxially with respect tosaid axis, said anode wall being substantially conical and beingpositioned adjacent the plasma cone emitted from low arc voltagematerial on the cathode wall.
 4. The electrical switch device of claim 3wherein said anode means has an annular body having an interiorfrusto-conical surface, said interior surface of said anode body havingits apex substantially at said high arc voltage material wall of saidcathode.
 5. An electrical switch device comprising: a vessel; condensermeans having a condensation surface within said vessel for condensingions and neutral particles in said vessel to maintain a sufficiently lowbackground pressure within said vessel during arcing that the atmospherein said vessel does not substantially interfere with arcing so that aconical plasma jet containing electrons, ions, and neutral particles isformed, so that electric arc discharge in a vacuum arc mode can bemaintained, said condensation surface being positioned in the path ofthe conical plasma jet; cathode means within said vessel for carrying alow arc voltage metal in sufficiently small area to minimize evaporationof low arc voltage metal from said cathode means into the atmospherewithin said vessel to permit said condenser means to mainTain thebackground pressure within said vessel during arcing sufficiently low sothat the plasma jet is an arc discharge in a vacuum arc mode; anodemeans within said vessel for interacting with said cathode means bycollecting electrons from the plasma jet so that an electric arcdischarge in a vacuum arc mode is maintained from the low arc voltagemetal on said cathode means to said anode means, said anode means beingformed with a conical anode wall defining an opening therethrough, withsaid anode wall positioned substantially tangent to the conical plasmajet so as to minimally perturb the ions and neutrals in the plasma coneand so as to electrically couple said anode structure with the plasmacone.
 6. The electrical switch device of claim 5 wherein: said condensermeans has a sufficiently large area with respect to the low arc voltagemetal area on said cathode means and being positioned with respect tosaid cathode means and said anode means for maintenance of thebackground pressure within said vessel during arcing outside of theconical plasma jet, at least as low as 10 3 Torr so that the arc occursin the vacuum arc mode and the atmosphere in said vessel does notsubstantially interfere with the conical plasma jet.
 7. The switchdevice of claim 6 wherein said condenser means has sufficiently largecondenser surface area with respect to the low arc voltage metal on saidcathode means and is maintained at least as low as about 263* K. so thatpressure within said vessel outside of the conical plasma jet is nothigher than about 10 3 Torr during arcing and not higher than about 10 4Torr during non-arcing.
 8. The electrical switch device of claim 7wherein said cathode means is operated so that the ratio of electrons toatoms within said conical plasma jet is at least as high as about fifty.9. The switching device of claim 5 wherein said surface on said anodemeans comprises a truncated hollow cone with its apex substantially atthe lower arc voltage metal on said cathode means.
 10. The process ofswitching an electric current comprising the steps of: maintaining avessel in which is positioned a condenser surface of sufficient size todominate the vapor equilibrium in said vessel at a reduced pressure bymaintaining the condenser surface at a reduced temperature; feedingliquid metal to a cathode in the vessel for conducting electric currentby arcing; cooling the condenser surface to a sufficiently reducedtemperature so that arcing which occurs between the cathode and an anodein the vessel is in a vacuum arc mode; discharging an arc between theanode and cathode which produces a plasma jet containing electrons, ionsand atoms with the ratio of electrons to atoms being at least 30-1; anddirecting the plasma jet through the anode toward the condenser so thatthe anode lies substantially tangent to the plasma jet so that the anodeis directly electrically coupled with the plasma jet for electron flowfrom the plasma jet to the anode.